Our proposed studies will use several different measurements of the lateral mobility of specific membrane proteins to study the lateral organization and dynamics of plasma membrane components. A major objective will be to further characterize the cytoplasmic and extracellular matrix factors which restrict the lateral mobility of components of animal cell membranes. These restrictions may affect not only the rate of lateral diffusion but also, in some instances, serve to confine the membrane protein to spatial domains. These studies will employ a major new tool, particle tracking microscopy, to directly visualize Brownian motion of single or small groups of proteins on the surface of single living cells. Efforts are proposed to further develop and establish this technology, including enhancing its time and spatial resolution. The technology will be applied to carefully characterize the motions and degree of confinement of specific transmembrane and lipid-linked membrane proteins. Direct testing of the "diffusion to a trap" mechanism of assembling specific structures in the plasma membrane is proposed. Lastly, a combination of the particle tracking technique, fluorescence recovery after photobleaching and gene transfer experiments will be applied to test a generalized working hypothesis of plasma membrane structure--the Transient Interaction Model. It is anticipated that information generated in this project will ultimately lead to a deepened understanding of plasma membrane organization in normal and diseased states.